Material and process for the filtration of nitric acid and NO2 from streams of air

ABSTRACT

A material for filtering NO 2  and nitric acid vapors from air over a wide range of humidities and temperatures including a porous hydrophobic substrate and an amine is provided.

TECHNICAL FIELD OF THE INVENTION

The present invention relates in general to the field of reducingenvironmentally harmful air pollutants and more specifically to a novelmaterial and process for filtering nitric acid vapors and NO₂ fromstreams of air.

BACKGROUND OF THE INVENTION

Both nitric acid vapors and NO₂ are highly toxic. The US Department ofLabor Occupational Safety and Health Administration (OSHA) has setstringent guidelines aimed at protecting workers performing operationsin an environment potentially contaminated with both fuming nitricacid/nitric acid vapors and NO₂. The Permissible Exposure Limit (PEL)for NO₂ has been established at 10 mg/m³ (approximately 5 ppm). ThePermissible Exposure Limit (PEL) for fuming nitric acid/nitric acidvapors has been established at 5.2 mg/m³ (approximately 2 ppm).

Impregnated, activated carbon is known to strongly adsorb a wide varietyof toxic vapors from ambient air streams. Impregnated, activated carbondoes not, however, effectively filter nitric acid vapors and NO₂ fromambient air streams. In the case of NO₂, there is no mechanismassociated with impregnated activated carbon capable of removing NO₂.NO₂ will, however, react with the surface of carbon to yield NO, whichrapidly elutes from the carbon bed. NO, like NO₂ is toxic. The PEL forNO has been established at 30 mg/m³ (approximately 25 ppm). Beingacidic, one would expect nitric acid vapors to be removed by impregnatedactivated carbon, such as those employed in military gas mask filters.Nitric acid vapors; however, are not removed by these filters becausenitric acid vapors react with the surface of activated carbon to yieldNO, which is toxic (PEL for NO has been established at 30 mg/m³,approximately 25 ppm).

Filtration media capable of removing NO₂ from streams of air is limited.Gooray et al. (U.S. Pat. No. 4,680,040) describe the use of alkali metalsilicates, specifically sodium silicate, lithium silicate and potassiumsilicate, to adsorb NO₂. The reaction is believed to involve the cationof the alkali metal silicate combining with NO₂ to form an alkali metalnitrate. Although data demonstrates this material to be effective infiltering low NO₂ concentrations (up to about 10 mg/m³), the materialdoes not appear to be able to filter high concentrations of NO₂ (1,000mg/m³).

Onitsuka et al. (U.S. Pat. No. 5,158,582) describe the use of coppersalts (CuCl, CuCl₂, CuCl₂.[NH₄Cl]₂) impregnated into zeolites to filterNO_(x) (mixtures of NO and NO₂). The copper impregnated zeolites areused to remove low levels of NO_(x) (about 10 mg/m³) present in highwaytunnels (from automotive exhaust). Up to 140 minutes of service life isreported for 10 mg/m³ challenge and 1 mg/m³ breakthrough. The patentnotes that humidity in the air greatly reduces the performance of thematerial, and the process described within the patent consists of an airdrier up-stream of the NO_(x) adsorber.

Ichiki et al. (U.S. Pat. No. 5,840,649) describe the use of a Mn dopedTiO₂ impregnated with either Ru or Cu oxide, plus Ag, Cu or additionalMn. The material is reported to be useful in treating low levels (about10 mg/m³) of NO_(x) from moist air streams.

Amines are known to interact with NO₂. A possible reaction betweenamines and NO₂ has been reported by Diaf et al. (J. Appd. Polymer Sci.53 (1994) 857) and Gaden (AIChE Symposium Series No. 309 (1995) 49–60).This reaction is presented below:RNH₂+NO₂→RN—NO+H₂O

However, under conditions of high relative humidity, the amine-NO₂reaction is minimized because pores of many adsorbents, such as carbon,become saturated with water. For toxic vapors such as NO₂ that are nothighly soluble in water, the presence of water in the pores of theadsorbent greatly decreases the performance of the filtration media.

Therefore, none of these previous solutions provide an effective, lowcost means of removing both nitric acid vapors and NO₂ from ambientstream of air under varying temperatures and humidities.

SUMMARY OF THE INVENTION

The present invention is, according to an embodiment, directed to amaterial for filtering NO₂ and nitric acid vapors from air over a widerange of humidities and temperatures includes a porous hydrophobicsubstrate and an amine. The porous hydrophobic substrate includeszeolites from the pentisil family. In one embodiment of the presentinvention, the zeolite is ZSM-5. In other embodiments the poroushydrophobic substrate may include ZSM-8, ZSM-11, and acidified forms ofzeolites of the pentisil family. The amine may include a primary amine,a secondary amine, an amine possessing both a primary and secondaryamine, and mixtures thereof. The amine may also include amine salts andamines with at least one R—NHCH₃ functional group. According to oneembodiment, the material includes from about 0.001% to about 20% byweight amine.

According to another embodiment of the present invention, a process forfiltering NO₂ and nitric acid over a wide range of humidities andtemperatures includes providing an amine impregnated porous hydrophobicsubstrate and an air stream and contacting the air stream with the amineimpregnated porous hydrophobic substrate. The process may operate underrelative humidities from 0% to 90% and temperatures from 0° F. to 120°F.

DETAILED DESCRIPTION OF THE INVENTION

The present invention, according to certain embodiments, relates to anovel material and the use of the novel material in a novel process forremoving NO₂ and nitric acid vapors from ambient air streams over a widerelative humidity (RH) range, from less than about 10% RH to greaterthan about 80% RH over a temperature of about 75° F.±about 50° F.

The novel material, in one embodiment, includes a porous hydrophobicsubstrate. In another embodiment, the porous hydrophobic substrate is azeolite from the pentisil family, preferably zeolite ZSM-5. ZSM-5,because of its commercial availability, is the preferred zeolite. ZSM-5is a high silica zeolite including a series of interconnecting paralleland sinusoidal channels approximately 5.8 Å in diameter. Preparation ofZSM-5 was first reported in U.S. Pat. No. 3,702,886. ZSM-5 is a memberof the pentisil family of zeolites that includes zeolitic materialswhose structure includes 5-membered rings. Additional common zeolitesbelonging to the pentisil family include ZSM-8 and ZSM-11. ZSM-5 may beprepared over a range of SiO₂/Al₂O₃ ratios, from greater than about10,000 to less than about 20. Because of its high silica content andsmall pores, ZSM-5 is hydrophobic, adsorbing a relatively small amountof water under high relative humidity conditions.

ZSM-5 crystals are synthesized in the sodium form and can be used asprepared, provided the as-synthesized zeolite is calcined to remove theorganic templating agent. Alternatively, ZSM-5 can be cation exchangedto a variety of forms, such as H—, Ca—, K—, etc., following proceduresknown to one skilled in the art.

The pores of the porous hydrophobic substrate may be impregnated witheither a primary or secondary amine, or mixture thereof, or a compoundcontaining both a primary and secondary amine functional group, forexample diethylenetriamine. According to one embodiment of the presentinvention, the amine is a primary amine, possessing an H₂N—R functionalgroup. According to another embodiment, the amine is a secondary amine,preferably possessing at least one H₃C—NH—R functional group.

The amine loading will have a significant impact on the performance ofthe resulting material. Based on the desired performance for thematerial, the amine loading can vary over a wide range, from as littleas about 0.01% by weight to as much as about 20% by weight. In oneembodiment, the amine loading may range from about 0.01% to about 5% byweight. In another embodiment, the amine loading may range from about 5%to about 10% by weight. In yet another embodiment, the amine loading mayrange from about 10% to about 15% by weight. In another embodiment, theamine loading may range from about 15% to about 20% by weight. Foroptimum performance, the preferred amine loading is from about 2% toabout 12% by weight, with an amine loading from about 5% to about 10% byweight being most preferred.

The novel material described herein involves first preparing particles,beads, spheres, etc., of preferably zeolite ZSM-5 followed byimpregnation of the particles with an amine solution. Followingimpregnation, the amine impregnated zeolite particles are dried toremove excess solution. Zeolite ZSM-5 may be purchased from commercialsources. Alternatively, zeolite ZSM-5 may be synthesized usingtechniques known to one skilled in the art (see for example U.S. Pat.No. 3,702,886). As prepared, ZSM-5 is a powder consisting of crystalstypically less than about 50 μm in length. As-synthesized ZSM-5 isgenerally neutral or mildly basic. Zeolite ZSM-5 may be employed in theacidified form, such as ion exchange with ammonium salts (e.g. ammoniumchloride) followed by calcinations.

Zeolites of the pentisil family, such as ZSM-5, can often be preparedover a wide range of SiO₂/Al₂O₃ ratios, from as low as about 20 togreater than about 10,000. However, the preferred SiO₂/Al₂O₃ ratio isbetween about 50 and 500, with a SiO₂/Al₂O₃ ratio between about 75 andabout 120 being more preferred.

As-synthesized zeolite of the pentisil family, such as ZSM-5, exists assmall crystals and must therefore be configured in the form ofparticles, rings, cylinders, spheres, etc. in order to be effectivelyemployed in the process described herein. Alternatively, pentisilzeolite such as ZSM-5 may be configured as a monolith, or coated ontothe walls of a ceramic material, for example honeycomb corderite.Failure to configure pentisil zeolite crystals, such as ZSM-5 crystals,as described above may result in excessive pressure drop across thefiltration media. Configuring the zeolite crystals into variousgeometrical shapes can be performed using techniques well known to oneskilled in the art. These techniques include pilling, extruding, etc.Binders, for example clays, silicates, plastics, etc., may or may not berequired for the given process; however, the use of binders in theformation of zeolite particles, spheres, etc, is preferred.

The acidified forms of other zeolites of the pentisil family, forexample H-ZSM-8 and H-ZSM-11. are also hydrophobic and therefore areexpected to function as a filtration media as per the present invention.However, ZSM-5 is the preferred filtration media.

Amine impregnation of pentisil zeolite particles, such as ZSM-5, areaccomplished using techniques well known to one skilled in the art, forexample incipient wetness. Impregnation involves adding the desiredamount of primary or secondary amine, or mixtures thereof, to a solvent,such as water. The amine-laden solvent is then contacted with the ZSM-5particles. Following contact, it is desired that the particles betreated, for example by drying at an elevated temperature, in order toremove the solvent.

Alternatively, primary or secondary amine, or mixtures thereof, can beadded to the ZSM-5 particles by evaporative techniques. For example,zeolite can be added to a rotating blender, and the amine can be slowlyadded to the blender while mixing.

According to one embodiment of the novel process described herein,ambient air laden with either nitric acid vapors, NO₂ or mixturesthereof, is passed through an amine impregnated hydrophobic substrate.The novel material employed in the process may include ZSM-5, ZSM-8, orother members of the pentisil zeolite family, impregnated with smallamounts of primary amine or secondary amine, or mixtures thereof.Examples of secondary amines include 1,3 dimethylurea (CH₃NHCONHCH₃) andN,N′ dimethylethylenediamine (CH₃NHC₂H₄NHCH₃). Examples of primaryamines include 1-3 diaminopropane (NH₂C₃H₆NH₂) and urea (H₂NCONH₂). Inaddition, the amine impregnant may include a compound possessing bothprimary and secondary amine functionalities, for examplediethylenetriamine (H₂N—C₂H₄—NH—C₂H₄—NH₂). Amines may also include aminesalts and amines with at least one R—NHCH₃ functional group.

According to one embodiment of the present invention, the processincludes the use of a porous hydrophobic substrate, such as ZSM-5, intowhich the reactive amine or mixture thereof are impregnated. Dependingon the environment and environmental conditions, the water contentassociated with ambient air may vary over a wide range, from about 0% togreater than about 90% relative humidity (RH). In one embodiment, theprocess occurs in conditions from about 0% RH to about 18% RH. Inanother embodiment the process occurs in conditions from about 18% RH toabout 36% RH. In yet another embodiment the process occurs in conditionsfrom about 36% RH to about 54% RH. In one embodiment, the process occursin conditions from about 54% RH to about 72% RH. In another embodiment,the process occurs in conditions from about 72% RH to about 90% RH.Zeolite ZSM-5, and other members of the pentisil zeolite family, ishydrophobic in nature, adsorbing only small amounts of water fromambient air streams under conditions of high relative humidity. As aresult, under conditions of high relative humidity, ambient moisture isnot significantly adsorbed and therefore does not significantly reducethe ability of the amine impregnated zeolite to filter NO₂ and nitricacid vapors.

Another embodiment of the present invention allows the process tooperate under a range of temperatures. In one embodiment the processoccurs in temperatures from about 0° F. to about 25° F. In anotherembodiment, the process in temperatures from about 25° F. to about 50°F. In yet another embodiment the process occurs in temperatures fromabout 50° F. to about 75° F. In one embodiment the process occurs intemperatures from about 75° F. to about 100° F. In another embodiment,the process in temperatures from about 100° F. to about 125° F.

According to one embodiment of the novel process described herein, theambient air stream containing NO₂, nitric acid vapors, or mixturesthereof, is passed through a filtration device in a manner that allowsfor contacting the contaminated process stream with the novel filtrationmaterial, preferably zeolite ZSM-5 impregnated with a secondary aminepossessing at least one H₃C—NH—R functional group. NO₂ and nitric acidvapors are removed from the ambient air stream via interaction withamine located within the pores of the zeolite. The filtration deviceemploying preferably amine impregnated zeolite ZSM-5 can take on manyshapes and geometric forms depending upon the application, so long asthe filtration device promotes contact between the stream being treatedand the filtration media. The linear velocity by which the contaminatedprocess stream passes through the filter bed containing preferably amineimpregnated zeolite ZSM-5 will be a function of the many parameters, forexample the bed depth, the ambient concentration of NO₂, nitric acidvapors, or mixtures thereof, and the desired protection (breakthroughtime) one wishes to achieve. Examples of filtration devices include, forexample, gas mask canisters, respirators, filter banks such as thoseemployed in fume hoods, ventilation systems, etc. A blower motor, fan,etc. may be used as a means of forcing ambient air through thefiltration device, if desired.

According to another embodiment of the novel process described herein isexpected to also remove additional acid gases, for example Cl₂, HCl, HF,etc., from an ambient air stream, as the basic amine impregnant(s) areexpected to remove acid gases via acid-base reaction chemistry.

The novel material and novel process described herein may be applied tomany forms and configurations that facilitate the contact between thenovel filtration material described herein and a contaminated vaporstream. Examples include gas masks, fume hood ventilation filters,cartridge filters, etc. It is necessary, however, that the zeoliteimpregnated with either a primary or secondary amine, or mixturethereof, be configured within the filtration apparatus in a manner suchthat the stream containing either nitric acid vapors, NO₂, or mixturesthereof is brought into contact with the novel filtration material.

Test Description: Laboratory scale tests were performed to evaluate theability of the filtration media to remove NO₂ and nitric acid vaporsfrom ambient air streams. A description of the laboratory scale teststand follows: A stream of compressed air delivered from a mass flowcontroller is delivered to a water sparger located within a temperaturecontrolled water bath. A second stream of compressed, dry air (dew pointtemperature less than minus 20° F.) is delivered from a second mass flowcontroller and is blended with the humid air stream from the watersparger. The water content of the air stream is controlled bycontrolling flow rates of the two process streams. An NO₂/air mixture(approximately 5% NO₂ in air) is delivered to the process stream at ajunction downstream of the water sparger using a mass flow controller.The resulting NO₂/air stream of varying water content is delivered tothe filtration test assembly. The filtration test assembly includes aglass tube fitted with a small mesh screen sufficient to support the bedof filtration material. A portion of the effluent stream is delivered toa chemiluminescence NO—NO_(x) analyzer.

When performing test with nitric acid vapors, the nitric acid vaporswere delivered to the process stream by passing a dry air stream througha sparger cell containing nitric acid. The concentration of nitric acidvapors were determined by passing the effluent stream through a bed ofplatinum catalyst at approximately 500° C. The catalyst converted thenitric acid vapors to NO_(x), thereby allowing the feed and effluentstreams to be analyzed using an NO—NO_(x) analyzer.

When performing tests under conditions of high RH, the filtration mediawas pre-humidified overnight in an environmental chamber at 80° F., 80%RH. All tests were performed at 80° F. at either less than 5% RH or 80%RH. All NO₂ breakthrough times are reported corresponding to an effluentNO₂ concentration of 10 mg/m³, or an effluent NO concentration of 30mg/m³. All breakthrough times for nitric acid vapors are reportedcorresponding to an NO_(x) equivalent concentration of 5 ppm.

EXAMPLE I (COMPARATIVE)

ASZM-TEDA carbon having a surface area of approximately 900 m²/g wasobtained from Calgon Carbon Corporation (Pittsburgh, Pa.) as 20×40 meshgranules. 7.5 cm³ of carbon granules were placed within the test cell soas to produce a bed with the depth of 1.0 cm. The bed was exposed to aprocess stream containing 200 mg/m³ NO₂ and flowing at a linear velocityof 6.0 cm/s. The RH of the process stream was less than 5%, and thetemperature of the process stream was maintained at 80° F. (27° C.).Breakthrough, as NO, occurred in less than 3 minutes. Breakthroughoccurred as NO because NO₂ oxidized the surface of the carbon granules,reducing NO₂ to NO.

20×40 mesh ASZM-TEDA carbon granules were pre-humidified at 80° F. (27°C.), 80% RH overnight. The pre-humidified carbon granules were thenevaluated for their ability to filter NO₂ as described above, with theexception that the RH of the process stream was 80%. Breakthrough, asNO, occurred in less than 3 minutes.

The above example demonstrates that impregnated, activated carbon isunable to filter NO₂.

EXAMPLE II (COMPARATIVE)

ASZM-TEDA carbon having a surface area of approximately 900 m²/g wasobtained from Calgon Carbon Corporation (Pittsburgh, Pa.) as 20×40 meshgranules. 7.5 cm³ of carbon granules were placed within the test cell soas to produce a bed with the depth of 1.0 cm. The bed was exposed to aprocess stream containing 1,000 mg/m³ nitric acid vapors and flowing ata linear velocity of 6.0 cm/s. The RH of the process stream was lessthan 5%, and the temperature of the process stream was maintained at 80°F. (27° C). Breakthrough, as NO, occurred in less than 3 minutes.Breakthrough occurred as NO due to the nitric acid vapors oxidizing thesurface of the carbon granules.

The above example demonstrates that impregnated, activated carbon isunable to filter nitric acid vapors.

EXAMPLE III

400 g of ZSM-5 crystals with a SiO₂/Al₂O₃ ratio of 120 were added to aglass pan. To the zeolite crystals were added 300 g of colloidal silicasolution (40% SiO₂) and 10 g of a 20% zirconia oxynitrate solution. Theresulting paste was mixed to a uniform consistency. The resulting pastewas placed in a forced convection oven overnight at 80° C. Once dry, thesolid material was placed in a furnace and calcined by heating to 450°C. in two hours, with the 450° C. temperature maintained for 2 hours.The resulting material was allowed to cool, then crushed and sieved to12×30 mesh granules.

A solution prepared by adding 3.5 g of diethylenetriamine (DETA) to 26.5g of water was used to impregnate 30 g of the 12×30 mesh ZSM-5 granulesusing incipient wetness techniques. Following impregnation, theresulting particles were placed in an oven at 80° C. overnight in orderto remove the water. Following drying, the resulting material wasdetermined to be 11% DETA.

EXAMPLE IV

The 12×30 mesh 11% DETA/ZSM-5 particles as described in Example III wereevaluated for their ability to remove NO₂ from streams of dry and humidair. 15 cm³ of DETA/ZSM-5 particles were placed in a 3.1 cm diameterjacketed glass tube, resulting in a 2.0 cm deep bed of 12×30 meshparticles. The particles were exposed to a feed stream consisting of1,000 mg/m³ NO₂ in dry air (RH<10%) flowing at a linear velocity of 6.0cm/s. The NO₂ breakthrough time (to 10 mg/m³) was 102 minutes.

EXAMPLE V

15 cm³ of the 12×30 mesh 11% DETA/ZSM-5 particles as described inExample III were placed in an environmental chamber at 80° F., 80% RHovernight in order to pre-humidify the material. 15 cm³ ofpre-humidified DETA/ZSM-5 particles were placed in a 3.1 cm diameterjacketed glass tube, resulting in a 2.0 cm deep bed of 12×30 meshparticles. The particles were exposed to a feed stream consisting of1,000 mg/m³ NO₂ in dry air (RH=80%) flowing at a linear velocity of 6.0cm/s. The NO₂ breakthrough time (to 10 mg/m³) was 67 minutes.

EXAMPLE VI

3,030 g of ZSM-5 crystals with a SiO₂/Al₂O₃ ratio of 90 were added to aplastic pail. To the zeolite crystals were added 3,409 g of 20% zirconiaoxynitrate solution, 341 g of colloidal silica solution (40% SiO₂) and129 g of pseduo-boehmite. The resulting dough was blended using anoverhead mixer to a uniform consistency. Once mixed, the resulting doughwas placed in a forced convection oven overnight at 80° C. The resultingsolid material was placed in a furnace and calcined by heating to 525°C. in five hours, with the 525° C. temperature maintained for 4 hours.The resulting material was allowed to cool, then crushed and sieved to12×30 mesh granules.

A solution prepared by adding 4.0 g of urea to 36 g of water was used toimpregnate 50 g of the 12×30 mesh ZSM-5 granules using incipient wetnesstechniques. Following impregnation, the resulting particles were placedin an oven at 80° C. overnight in order to remove the water. Followingdrying, the resulting material was determined to be 8% urea.

A solution prepared by adding 0.6 g of urea to 38 g of water was used toimpregnate 50 g of the 12×30 mesh ZSM-5 granules using incipient wetnesstechniques. Following impregnation, the resulting particles were placedin an oven at 80° C. overnight in order to remove the water. Followingdrying, the resulting material was determined to be 1.3% urea.

EXAMPLE VII

The 12×30 mesh 8% urea/ZSM-5 particles as described I Example VI wereevaluated for their ability to remove NO₂ from streams of dry and humidair. 15 cm³ of urea/ZSM-5 particles were placed in a 3.1 cm diameterjacketed glass tube, resulting in a 2.0 cm deep bed of 12×30 meshparticles. The particles were exposed to a feed stream consisting of1,000 mg/m³ NO₂ in dry air (RH<10%) flowing at a linear velocity of 9.6cm/s. The NO₂ breakthrough time (to 10 mg/m³) was 110 minutes.

The 12×30 mesh 1.3% urea/ZSM-5 particles as described in Example VI wereevaluated for their ability to remove NO₂ from streams of dry and humidair. 15 cm³ of urea/ZSM-5 particles were placed in a 3.1 cm diameterjacketed glass tube, resulting in a 2.0 cm deep bed of 12×30 meshparticles. The particles were exposed to a feed stream consisting of1,000 mg/m³ NO₂ in dry air (RH<10%) flowing at a linear velocity of 9.6cm/s. The NO₂ breakthrough time (to 10 mg/m³) was 44 minutes.

EXAMPLE VIII

7.5 cm³ of 20×50 mesh 11% DETA/ZSM-5 granules prepared according to theprocedure described in Example III were placed in a in a 3.1 cm diameterjacketed glass tube, resulting in a 1.0 cm deep bed. The particles wereexposed to a feed stream consisting of 1,000 mg/m³ HNO₃ vapors in dryair (RH<10%) flowing at a linear velocity of 6.0 cm/s. The HNO₃breakthrough time (to 5.2 mg/m³) was 99 minutes.

EXAMPLE IX

7.5 cm³ of 20×50 mesh 11% DETA/ZSM-5 granules prepared according to theprocedure described in Example III were pre-humidified overnight in anenvironmental chamber at 80° F., 80% RH. The weight gain uponhumidification was 8%. In the morning, the pre-humidified material wasplaced in a in a 3.1 cm diameter jacketed glass tube, resulting in a 1.0cm deep bed. The particles were exposed to a feed stream consisting of1,000 mg/m³ nitric acid vapors in humid air (RH=50%) flowing at a linearvelocity of 6.0 cm/s. The HNO₃ breakthrough time (to 5.2 mg/m³) was 93minutes.

EXAMPLE X

500 g of ZSM-5 crystals with a SiO₂/Al₂O₃ ratio of 90 were added to amixing bowl. To the zeolite crystals were added 563 g of 20% zirconiaoxynitrate solution, 56 g of colloidal silica solution (40% SiO₂) and24.1 g of pseduo-boehmite. The resulting dough was blended using anoverhead mixer to a uniform consistency. Once mixed, the resulting doughwas placed in a forced convection oven overnight at 70° C. The resultingsolid material was placed in a furnace and calcined by heating to 550°C. in 2.5 hours, with the 550° C. temperature maintained for 4 hours.The resulting material was allowed to cool, then crushed and sieved to12×30 mesh granules.

A solution prepared by adding 1.5 g of N,N′ dimethylethylenediamine to24 g of DI water was used to impregnate 30 g of the 12×30 mesh ZSM-5granules using incipient wetness techniques. Following impregnation, theresulting particles were placed in an oven at 80° C. overnight in orderto remove the water. Following drying, the resulting material wasdetermined to be 4% N,N′ dimethylethylenediamine by weight.

EXAMPLE XI

The 12×30 mesh 4% N,N′ dimethylethylenediamine/ZSM-5 particles inExample X were evaluated for their ability to remove NO₂ from streams ofdry and humid air. 15 cm³ of N,N′ dimethylethylenediamine/ZSM-5particles were placed in a 3.1 cm diameter jacketed glass tube,resulting in a 2.0 cm deep bed of 12×30 mesh particles. The particleswere exposed to a feed stream consisting of 1,000 mg/m³ NO₂ in dry air(RH<10%) flowing at a linear velocity of 9.6 cm/s. The NO₂ breakthroughtime (to 10 mg/m³) was 95 minutes.

15 cm³ of 12×30 mesh N,N′ dimethylethylenediamine/ZSM-5 particles(Example X) were pre-humidified overnight at 80° F., 80% RH. The weightgain resulting from moisture pick-up was 7%. The pre-humidifiedparticles placed in a 3.1 cm diameter jacketed glass tube, resulting ina 2.0 cm deep bed. The particles were exposed to a feed streamconsisting of 1,000 mg/m³ NO₂ in humid air (RH=80%) flowing at a linearvelocity of 9.6 cm/s. Under humid test conditions, breakthrough occurredas NO, rather than NO₂. The NO breakthrough time (to 30 mg/m³) was 54minutes.

EXAMPLE XII

500 g of ZSM-5 crystals with a SiO₂/Al₂O₃ ratio of 90 were added to amixing bowl. To the zeolite crystals were added 563 g of 20% zirconiaoxynitrate solution, 56 g of colloidal silica solution (40% SiO₂) and24.1 g of pseduo-boehmite. The resulting dough was blended using anoverhead mixer to a uniform consistency. Once mixed, the resulting doughwas placed in a forced convection oven overnight at 70° C. The resultingsolid material was placed in a furnace and calcined by heating to 550°C. in 2.5 hours, with the 550° C. temperature maintained for 4 hours.The resulting material was allowed to cool, then crushed and sieved to12×30 mesh granules.

An aqueous amine solution was prepared by adding 3.0 g of 1,3 dimethylurea to 25 g of DI water. The resulting solution was used to impregnate30 g of the 12×30 mesh ZSM-5 granules using incipient wetnesstechniques. Following impregnation, the resulting particles were placedin an oven at 80° C. overnight in order to remove the water. Followingdrying, the resulting material was determined to be 8% 1,3 dimethyl ureaby weight.

EXAMPLE XIII

The 12×30 mesh 8% dimethyl urea/ZSM-5 particles in Example XII wereevaluated for their ability to remove NO₂ from streams of dry and humidair. 15 cm³ of dimethyl urea/ZSM-5 particles were placed in a 3.1 cmdiameter jacketed glass tube, resulting in a 2.0 cm deep bed of 12×30mesh particles. The particles were exposed to a feed stream consistingof 1,000 mg/m³ NO₂ in dry air (RH<10%) flowing at a linear velocity of9.6 cm/s. The NO₂ breakthrough time (to 10 mg/m³) was 61 minutes.

An additional 15 cm³ of 12×30 mesh 8% dimethyl urea/ZSM-5 particles(Example XII) were pre-humidified overnight at 80° F., 80% RH. Theweight gain resulting from moisture pick-up was 7%. The pre-humidifiedparticles placed in a 3.1 cm diameter jacketed glass tube, resulting ina 2.0 cm deep bed. The particles were exposed to a feed streamconsisting of 1,000 mg/m³ NO₂ in humid air (RH=80%) flowing at a linearvelocity of 9.6 cm/s. Under humid test conditions, breakthrough occurredas NO, rather than NO₂. The NO breakthrough time (to 30 mg/m³) was 91minutes.

EXAMPLE XIV

500 g of ZSM-5 crystals with a SiO₂/Al₂O₃ ratio of 90 were added to amixing bowl. To the zeolite crystals were added 563 g of 20% zirconiaoxynitrate solution, 56 g of colloidal silica solution (40% SiO₂) and24.1 g of pseduo-boehmite. The resulting dough was blended using anoverhead mixer to a uniform consistency. Once mixed, the resulting doughwas placed in a forced convection oven overnight at 70° C. The resultingsolid material was placed in a furnace and calcined by heating to 550°C. in 2.5 hours, with the 550° C. temperature maintained for 4 hours.The resulting material was allowed to cool, then crushed and sieved to12×30 mesh granules.

An aqueous amine solution was prepared by adding 3.0 g of ethylamine.HClto 23 g of DI water. The resulting solution was used to impregnate 30 gof the 12×30 mesh ZSM-5 granules using incipient wetness techniques.Following impregnation, the resulting particles were placed in an ovenat 80° C. overnight in order to remove the water. Following drying, theresulting material was determined to be 9% ethylamine.HCl by weight.

EXAMPLE XV

The 12×30 mesh 9% ethylamine.HCl/ZSM-5 particles in Example XIV wereevaluated for their ability to remove NO₂ from streams of dry and humidair. 15 cm³ of 9% ethylamine.HCl/ZSM-5 particles were placed in a 3.1 cmdiameter jacketed glass tube, resulting in a 2.0 cm deep bed of 12×30mesh particles. The particles were exposed to a feed stream consistingof 1,000 mg/m³ NO₂ in dry air (RH<10%) flowing at a linear velocity of9.6 cm/s. The NO₂ breakthrough time (to 10 mg/m³) was 27 minutes.

An additional 15 cm³ of 12×30 mesh 9% ethylamine.HCl/ZSM-5 particles(Example XIV) were pre-humidified overnight at 80° F., 80% RH. Theweight gain resulting from moisture pick-up was 14%. The pre-humidifiedparticles placed in a 3.1 cm diameter jacketed glass tube, resulting ina 2.0 cm deep bed. The particles were exposed to a feed streamconsisting of 1,000 mg/m³ NO₂ in humid air (RH=80%) flowing at a linearvelocity of 9.6 cm/s. Under humid test conditions, breakthrough occurredas NO, rather than NO₂. No NO₂ was detected in the effluent streamduring the test. The concentration of NO in the effluent streamincreased to 50 mg/m³ following 1 minute, then decreased to less than 30mg/m³ following 5 minutes of exposure. The effluent concentration of NOdid not exceed 30 mg/m³ until 56 minutes.

EXAMPLE XVI

500 g of ZSM-5 crystals with a SiO₂/Al₂O₃ ratio greater than 500 wereadded to a mixing bowl. To the zeolite crystals were added 563 g of 20%zirconia oxynitrate solution, 56 g of colloidal silica solution (40%SiO₂) and 24.1 g of pseduo-boehmite. The resulting dough was blendedusing an overhead mixer to a uniform consistency. Once mixed, theresulting dough was placed in a forced convection oven overnight at 70°C. The resulting solid material was placed in a furnace and calcined byheating to 550° C. in 2.5 hours, with the 550° C. temperature maintainedfor 4 hours. The resulting material was allowed to cool, then crushedand sieved to 12×30 mesh granules.

An aqueous amine solution was prepared by adding 3.0 g of 1,3 dimethylurea to 25 g of DI water. The resulting solution was used to impregnate30 g of the 12×30 mesh ZSM-5 granules using incipient wetnesstechniques. Following impregnation, the resulting particles were placedin an oven at 80° C. overnight in order to remove the water. Followingdrying, the resulting material was determined to be 8% 1,3 dimethyl ureaby weight.

EXAMPLE XVII

The 12×30 mesh 8% dimethyl urea/ZSM-5 particles in Example XVI wereevaluated for their ability to remove NO₂ from streams of dry. 15 cm³ of8% dimethyl urea/ZSM-5 particles were placed in a 3.1 cm diameterjacketed glass tube, resulting in a 2.0 cm deep bed of 12×30 meshparticles. The particles were exposed to a feed stream consisting of1,000 mg/m³ NO₂ in dry air (RH<10%) flowing at a linear velocity of 9.6cm/s. The NO₂ breakthrough time (to 10 mg/m³) was 90 minutes.

EXAMPLE XVIII

The 12×30 mesh 8% dimethyl urea/ZSM-5 particles in Example XII areevaluated for their ability to remove Cl₂ from streams of dry air. 15cm³ of dimethyl urea/ZSM-5 particles are placed in a 3.1 cm diameterjacketed glass tube, resulting in a 2.0 cm deep bed of 12×30 meshparticles. The particles are exposed to a feed stream consisting of1,000 mg/m³ Cl₂ in dry air (RH<10%) flowing at a linear velocity of 9.6cm/s. The Cl₂ breakthrough time (to 10 mg/m³) is greater than 60minutes.

1. A process for filtering NO₂ and nitric acid vapors from air over widerange of humidities and temperatures comprising: providing an amineimpregnated porous hydrophobic substrate and an air stream; andcontacting the air stream with the amine impregnated porous hydrophobicsubstrate.
 2. The process of claim 1 wherein the amine impregnatedporous hydrophobic substrate comprises a zeolite from the pentisilfamily containing from about 0.001% to about 20% by weight amine.
 3. Theprocess of claim 1 wherein the amine impregnated porous hydrophobicsubstrate comprises an amine selected from the group consisting of aprimary amine, a secondary amine, an amine possessing both a primary andsecondary amine functional group and mixtures thereof.
 4. The process ofclaim 1 wherein the amine impregnated porous hydrophobic substratecomprises ZSM-5.
 5. The process of claim 1 wherein the amine impregnatedporous hydrophobic substrate comprises a zeolite selected from the groupconsisting of ZSM-5, ZSM-8, ZSM-11 and mixtures thereof.
 6. The processof claim 1 wherein said amine is predominantly an amine salt.
 7. Theprocess of claim 1 wherein the process operates under conditions fromabout 0% to about 90% relative humidity.
 8. The process of claim 1wherein the process operates under a temperature from about 0° F. toabout 125° F.
 9. A process for filtering NO₂ and nitric acid vapors fromair comprising: providing a zeolite and an air stream, wherein thezeolite is from the pentisil family and comprises from about 0.001% toabout 20% by weight an amine selected from the group consisting of aprimary amine, a secondary amine, an amine possessing both a primary andsecondary amine functional group, and mixtures thereof; and; contactingthe air stream with the zeolite.
 10. The process of claim 9 the zeolitecomprises predominantly ZSM-5.
 11. The process of claim 9 the aminecomprises predominantly an amine salt.